The European Extremely Large Telescope is indeed extremely large with a diameter of 39 meters.
ESO
An astronomy organization made up of 15 European countries, as well as Chile and Brazil, has signed a €400 million ($450 million) contract to proceed with the construction of a large dome and structure to support a massive optical telescope that will 39-meter wide main mirror.
The European Southern Observatory said the contract is on track to begin observing the night sky with its European Extremely Large Telescope (EELT) as early as 2024. The telescope will operate from a 3,000-meter mountain peak in northern Chile. The agency said this is the most expensive contract ever awarded by ESO and the largest contract ever awarded in ground-based astronomy. However, it represents only a fraction of the telescope’s multi-billion dollar total cost.
The largest optical telescopes in the world today are only about 10 meters in diameter. The European instrument is part of a new generation of much larger telescopes being built to better enable astronomers to look further back into the history of the universe, when the first stars and galaxies formed. The newly possible observations could also elucidate the nature of dark matter and dark energy, and possibly detect traces of life in the atmospheres of exoplanets. As such, there is a great race to reach first light and start using these great instruments. Nobel Prizes await.
A consortium of US and international institutions has begun construction of the 24.5-meter Magellan telescope in Chile, which may be operational as early as 2023. Another group of largely US-based institutions is trying to build the Thirty Meter telescope in Hawaii, but Native Hawaiians are protesting the facility atop Mauna Kea, saying it desecrates sacred ground. The protests have delayed construction.
No similar concerns have been raised in Chile about the EELT or the Giant Magellan Telescope, so for both groups the race to the finish is largely about raising funds in excess of $1 billion and ensuring their complicated instruments function as intended – no small matter in building the world’s most powerful telescopes.